U.S. Pat. No. 5,466,988 has already disclosed an electric lamp which has a spherical discharge vessel made from quartz glass. An insert part made from ceramic, for example a tube, is arranged axially in the interior of the discharge vessel and is intended to suppress convection. It has a retaining device which is formed, for example, from rings at the ends of the tube, the rings being supported in a resilient manner on the outer wall.
This arrangement is very complex and susceptible to errors, since separate retaining parts first need to be mounted on the insert part, and this unit needs to be introduced carefully into the discharge vessel. The circular discharge vessel means that axial fixing is considered to be necessary and that this is implemented by means of separate knobs on the inner wall. This design is therefore extremely expensive.